Technical Bulletin Oct 08 Conformal Coating Failure Mechanisms Cracking

     

 

Technical Bulletin Oct 08 Common failure mechanisms in conformal coating: Cracking In conformal coating, there are several mechanisms that cause failure of printed circuit boards (PCBs). In a series of technical bulletins SCH will examine the common failure mechanisms in conformal coating including capillary flow, delamination, cracking, loss of adhesion, dewetting, corrosion, orange peel, pin holes, bubbles and foam.

Conformal Coating Failure Mechanism: Cracking Definition Cracking in conformal coating is where a smooth surface fractures into sections with the cracks in the coating leaving the area below exposed to potential contaminants. Causes of Cracking in Conformal Coating Factors that influence cracking include:

 

1. Cure temperature too high 2. Conformal coating heat cured too quickly without allowing enough time for room temperature (RT) drying 3. Film thickness too great causing coefficient of thermal expansion (CTE) mismatch and cracks occurring in the coating 4. Operating temperature too high or too low causing the conformal coating to flex too much & crack.   SCH Technologies is a Trading Name of SCH Services Limited  Newburgh Building, McLintock Way, Barnsley, South Yorkshire. S70 6BF    Tel: +44 (0)1226 297711 Fax: +44 (0)1226 297733  www.conformalcoating.co.uk 

Examples of Conformal Coating Cracking

 

SCH Technologies are ISO9001 and ISO14001certified

          Examples of Cracking Effects Examples are shown in the images throughout the bulletin where the conformal coating has cracked, potentially allowing contaminants to the board surface.

 

How to stop Cracking in Conformal Coating It is possible to minimise conformal coating racking effects by •

Lowering the initial cure temperature

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Allowing an initial drying time at room temperature before exposure to elevated temperature

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Reducing the coating thickness to avoid CTE mismatch issues

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Select a coating with a wider temperature range performance.

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Examples of Conformal Coating Cracking

Select a more flexible coating SCH Technologies offer

Future Bulletins Common Conformal Coating Failure Mechanisms covering delamination, loss of adhesion, dewetting, corrosion, orange peel, pin holes, bubbles and foam.

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Conformal coating Subcontract Services

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Conformal Coating Application Equipment

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Humiseal Conformal Coatings

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Conformal Coating Training courses

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Conformal Coating Consultation & troubleshooting PLEASE CHECK OUR WEBSITE FOR DETAILS

SCH Technologies is a Trading Name of SCH Services Limited  Newburgh Building, McLintock Way, Barnsley, South Yorkshire. S70 6BF    Tel: +44 (0)1226 297711 Fax: +44 (0)1226 297733  www.conformalcoating.co.uk 

SCH Technologies are ISO9001 and ISO14001certified